George and Barbara Bush never stopped agonizing over Robin, their 3-year-old who died in 1953

Courtesy George Bush Presidential Library

Robin Bush in Greenwich, Conn., in June 1953.

Robin Bush in Greenwich, Conn., in June 1953.

(Courtesy George Bush Presidential Library)

Michael Brice-Saddler and Steve HendrixWashington Post

In a letter penned to his mother in the late 1950s, George H.W. Bush indicated that something was missing from his home.

At the time, Bush and his wife, Barbara, were parents to four rambunctious young boys - George W., Jeb, Marvin and Neal - whom they loved dearly. But, he wrote, there was something he still longed for.

Something he once had.

"The running, pulsating restlessness of the four boys as they struggle to learn and grow - needs a counterpart," he wrote. "We need some starched crisp frocks to go with all our torn-kneed blue jeans and helmets. We need some soft blond hair to offset those crew cuts. We need a doll house to stand firm against our forts and rackets and thousand baseball cards."

He continued, "We need a girl."

For a few years, Pauline Robinson "Robin" Bush was that girl. Once expressive and energetic like her brothers, young Robin in 1953 began to complain that she felt tired. Barbara took her to a pediatrician.

The doctor called a few days later with devastating news: Robin was very sick. She had leukemia - a word the Bushes had never heard before - and the prognosis was bleak: The 3-year-old would not survive.

"Her advice was to tell no one, go home, forget that Robin was sick, make her as comfortable as we could, love her - and let her gently slip away," Barbara Bush wrote in her 1994 memoir. "She said this would happen very quickly."

Instead, the Bushes began a months-long fight to keep their daughter alive.

The day after getting the bad news, the Bushes flew with Robin from their home in Midland, Texas, to New York, moving into the apartment of George H.W. Bush's grandparents on Manhattan's East Side. His uncle was a doctor at Sloan Kettering, a leading cancer center even when cancer was barely understood and considered taboo to speak about.

Robin stayed in the hospital for seven months, having regular bone-marrow tests and blood transfusions. USA Today reporter Susan Page, who is penning a biography of Barbara Bush set to be published next year, writes that Barbara had one rule - no crying in Robin's room.

This was a rule that George H.W. Bush - who was sentimental and routinely wore his emotions on his sleeve - found nearly impossible to comply with.

He would tell Robin that he had to go to the bathroom when he felt the tears coming, Page reports. But he would actually step into the hallway to gather himself. Seeing his sick daughter, whom he would describe in the letter to his mother as a "legitimate Christmas angel," was agonizing at times.

"We used to laugh and wonder if Robin thought he had the weakest bladder in the world," Barbara Bush later said, according to Page. "Not true. He just had the most tender heart."

Page writes that Barbara collapsed into sorrow when Robin breathed her last and that it was her husband who helped her regain her composure. Later, Barbara would marvel that a tragedy that splits many couples had brought them closer.

"Time after time during the next six months," she said, "George would put me together again."

George H.W. Bush would remain sensitive to the disease throughout his life. Upon winning a seat in the House in 1966, Bush began exchanging letters with Paul Dorsey, a constituent in Houston who had voted for his opponent. When Dorsey was diagnosed with cancer, Bush visited him in the hospital.

While eulogizing the former president on Wednesday, Bush's biographer, Jon Meacham, recalled an instance when Bush cried upon meeting a young boy in Krakow, Poland, who had leukemia:

"As vice president, Bush once visited a children's leukemia ward in Krakow. Thirty-five years before, he and Barbara had lost a daughter, Robin, to the disease. In Krakow, a small boy wanted to greet the American vice president. Learning that the child was sick with the cancer that had taken Robin, Bush began to cry," Meacham said.

He continued: "To his diary later that day, the vice president said this: 'My eyes flooded with tears. And behind me was a bank of television cameras. And I thought, 'I can't turn around. I can't dissolve because of personal tragedy in the face of the nurses that give of themselves every day.' So I stood there looking at this little guy, tears running down my cheek, hoping he wouldn't see. But if he did, hoping he'd feel that I loved him.' "

At the National Book Festival in 2016, while discussing the letter that Bush wrote to his mother about Robin's death, Meacham indicated that he once had Bush read it aloud.

Long before he could finish, Meacham said, Bush broke down in sobs so piercing that it prompted his chief of staff to enter the room.

"Why did you want President Bush to do that?' " she asked.

"If you want to know someone's heart," Meacham began to reply - but the president interrupted him.

"You have to know what breaks it," Bush added.

On Thursday, Bush will be buried between Robin and Barbara at his presidential library in College Station, Texas.